Firearms and Fingerprints

TVLiesWe’ve all seen the show.

COP: “We recovered the murder weapon, it had your fingerprints on the trigger!”

CRIM: “Uh, you got me. I did it! And you’ll never take me alive, copper!”

SFX Contagious Firing.

CRIM falls dead. COP and PARTNER high-five.

ROLL CREDITS

And that’s just the way it happens, right? Er, not right. While TV fingerprints relentlessly follow the laws of screenwriting, real fingerprints respond to the laws of physics. Even if the criminal took no measures to hide his fingerprints, they are a lot rarer and harder to recover than most people know.

fingerprint-3This is a separate question from whether fingerprint IDs are accurate. A small study sponsoed by the National Academy of Sciences found a 7.5% false negative rate, and a 0.1% false positive rate, in testing of actual print examiners. If the study is representative, 1 in 1000 print identifications is wrong. Most defense attorneys know better than to challenge that: jurors, too, watch CSI: Laboratory Magick and other TV shows.

And this is a separate question from whether the examiner is working honestly, or falsifying evidence, as a string of recent scandals shows.

Ed Hueske of the University of North Texas, in Firearms and Fingerprints, one of a 7-volume set of  popular books on forensic science published by Facts on File, generally cheerleads for the modern beau ideal of the forensic technician as a putatively objective scientist who just happens to be a full member of the police-prosecution team. But even he notes:

It is widely accepted as unlikely, for example, that identifiable fingerprints will be found on firearms. Identifiable fingerprints will be found probably less than 10 percent of the time. 1

And…

In the author’s experience identifiable fingerprints are found on guns, knives, clubs, and the like in less than 10 percent of the cases. This is due to a number of factors including the surface characteristics of the weapon and the way in which the weapon was handled. On the other hand it is not uncom- mon to find some evidence of the handling of weapons in the form of partial fingerprint impressions, even though these partial impressions usually fall short of being identifiable to a specific individual.
Some types of evidence simply do not tend to retain any evidence of fingerprints, even when touched. Textured surfaces such as vehicle steering wheels, plastic milk jugs, and suitcase handles seldom show any sign of even having been touched. Other problems can include intense heat, humidity, and/or precipitation, which effectively destroy the fin- gerprints. Thus the probability of finding identifiable fingerprints on fired cartridge cases left at the crime scene, for example, is remote; the combination of the curved surfaces and the heat produced upon discharge tends to vaporize the fingerprints.2

Malvo was implicated as a shooter through a fingerprint found on the weapon and a fingerprint found on a cartridge case near one of the scenes. Finding identifiable fingerprints on weapons and fired cartridge cases is pretty uncommon, making this a stroke of good luck for investigators.3

He goes on to caution:

When a suspect’s fingerprints are not found on a murder weapon, however, defense attorneys often present this fact as an indication of their client’s innocence.

Likewise, the forensic scientist must take care not to inflate the significance of the physical evidence that is present. For instance, investigation might turn up a partial fingerprint that cannot be positively identified as belonging to a particular individual. To describe such a print as “consistent with” having been made by a suspect without explaining the other possibilities (namely that numerous other persons could be responsible) would be misleading.4

Many of the practitioners of this art seem untroubled by the possibility of their testimony being misleading. Some of them will even testify that not finding fingerprints on a firearm (where we have just learned that they are unlikely to be found is evidence in itself, of “conspicuous absence.”

…in the investigation of shooting deaths, the question of suicide versus homicide often comes up. If iden- tifiable fingerprints actually happen to be present on a weapon and they do not belong to the victim, homicide might be indicated. On the other hand, if fingerprints are conspicuous by their absence, further investigation is warranted.5

And Huelske goes on to reiterate that fingerprints are seldom found on guns or other weapons, and what this means:

While juries are often persuaded to believe that fingerprints would have to be left on a gun or a knife if a person handled it, nothing could be further from the truth. Consider, for example, weapon design. The surfaces that are typically handled on weapons are by design textured so as not to be slippery. While it is certainly possible to leave a finger- print on a weapon, in many instances it almost requires an overt effort to do so. Likewise, if a person had just washed and dried his or her hands prior to handling a weapon, it would be improbable that any fin- gerprints would be deposited. While it is still important always to test a weapon for fingerprints and not simply assume none will be found, it is more likely than not that the weapon will bear no fingerprints.

There are all sorts of explanations for why evidence might not be found, such as the following:

• It was never there to begin with.
• It was present but was removed prior to testing.
• The testing was improperly carried out.

The real point, again, is that negative evidence of any sort has no real significance beyond the fact that it was not found.6

Fingerprint evidence is very important to crime fighting. It works because most criminals start with small crimes and work their way up, so by the time they commit a crime that’s worth collecting fingerprint evidence at — as many outraged home owners and business managers have found, this usually isn’t a burglary or other property crime, but because it’s one of the forms of self-incrimination not protected by the Constitution. (Only speech-related testimonial self-incrimination falls under the 5th Amendment exclusion; physical self-incrimination, such as by fingerprint, DNA, handwriting, etc. is excepted).7

But fingerprint evidence is not magic, and it’s not readily recovered from guns; and that recovery is preventable with simple precautions, which are unfortunately taught from criminal to criminal in prison, and easily enough deduced by a reasonably intelligent person who investigates how fingerprint evidence is collected, developed and evaluated.

In fact, they’re more likely (if they try) to recover fingerprints from inside disposable gloves used by a criminal, than from a pistol handled directly by that criminal with bare hands. Food for thought, and that much more evidence that TV crime and investigation shows are made by people unfamiliar with crime or investigation.

Notes

  1. Hueske, p. xvii
  2. Hueske, p. 2.
  3. Hueske, p. 12.
  4. Hueske, p. xvii-xviii.
  5. Hueske, p. 15.
  6. Hueske,
  7. Del Carmen, pp. 370-371, 474-475, G-7.

Sources

Del Carmen, Rolando V. Criinal Procedure: Law and Practice, 7/e. Belmont, CA, 2007: Thomson Higher Education. (This is a very dry criminal law textbook).

Hueske, Edward. Firearms and Fingerprints. New York, 2009: Facts on File. (Note that this isn’t a book on finding fingerprints on firearms, exclusively. It covers both fingerprint examination, including prints on firearms and other weapons, and  firearms examination, a completely different discipline.

 

24 thoughts on “Firearms and Fingerprints

  1. ToastieTheCoastie

    Interesting post Hognose. Apparently prosecutors are finding it more difficult to get convictions because modern juries expect all the evidence to get tied together in one neat little package, just like Law & Order.

  2. Jim Scrummy

    You mean crimes are not solved ala CSI something or NCIS something? I’m shocked, that evidence can’t be wrapped up at a crime scene with an arrest/capture/gunfight (where no-one runs out of those bullet thingeys) of the perp, in 40 minutes or less on the teevee.

  3. Gray

    The difficulty of retrieval notwithstanding, there has been at least one case that challenged fingerprint reliability per Daubert (http://www.nasams.org/forensics/for_lib/Documents/1036603149.93/Plaza2.htm)

    As a refresher for anyone who cares, “Daubert” requires passing a 5 part test before evidence can be accurately deemed scientifically reliable:

    (1) whether the evidence can be (and has been) tested” using the scientific method;
    (2) whether it has been subjected to peer review and publication;
    (3) the known or potential rate of error of the technique in question;
    (4) the existence and maintenance of standards controlling the technique’s operation;
    (5) the general acceptance of the technique within the relevant scientific community.

  4. Miles

    While it’s also just an hour long TV show, the series 48 Hours (the homicide version) actually is interesting.

    Not just because the we can see what demographic is most usually involved in the larger cities, but also how ‘real’ police investigations work.

    Fingerprints seem to very rarely be a part of the investigation. Even when guns used are found (again very rare), ballistic forensics and serial number tracing never seems to be mentioned in detail.

    The pepper-traitors are mostly figured out from street informants, or security video, and then when questioned, very rarely exercise their right to shut up and talk themselves right into it and quite often just finally confess.

    Many others who do ‘clam up”, after being charged just plead out. It’s like everybody knows the drill and plays their part.

    1. Hognose Post author

      The one you’re thinking of is The First 48. One of the few TV shows I will turn on. Of course, I’m usually only in front of the TV to act as a buffer between a reclined recliner and a sleeping Small Dog.

  5. Law of Self Defense

    Speaking as an attorney with some experience dealing with forensic evidence, as well as someone with some modest graduate-level scientific training in molecular biology, there are enormous swaths of forensic “science” that are utter crap. Virtually none of it is actual “science” at all, but just an amalgamation of “sciency-sounding” anecdotal observations. Virtually none of this stuff is validated to anything like the level that would be expected of any product or service used for a serious purpose–say, flight or bridge engineering.

    Of course, genuine science of any sort is getting pretty hard to come by these days. The Dark Ages beckon once again.

    –Andrew, @LawSelfDefense

    1. Hognose Post author

      The NAS did a study some time ago that came to broadly similar conclusions. The fingerprint study I linked to had “only” a 0.1% false positive rate (for the FP analyst’s part of the puzzle, only). It is the only scientific method study I’ve seen on fingerprint identification.

      “Firearms analysis” and “tool-mark analysis” are intermediate between fingerprints (usually right) and bite-mark analysis (usually wrong). Probably about where polygraphy is (equivalent to a coin toss).

      HAmmer-forged barrels leave few to no toolmarks, yet firearms examiners testify that this bullet is “consistent with” that Glock all the time. None of them has ever taken a double-blind test to the best of my knowledge. “Consistent with the suspect’s/officer’s Glock?” Sure. And with thousands of serial numbers on either side of it, in the same caliber. ‘

      They’re now coming out with 3D ballistic scanners… not to be more reliable, but to make more convincing whiz-bang graphics that can be used to sway the jury.

      1. Toastrider

        I remember reading about the bite-mark guy. Good grief, what a mess.

        Something I think people often miss, too: if a forensic lab’s analysis turns out to be tainted, what are the chances that any conviction associated with that lab is ripe to be overturned? I’d put good odds on it.

      2. Aaron Spink

        So on this topic, last night’s episode of Adam Ruins Everything was on forensic science. Well worth it if you can find either on TruTV or other methods. As an aside, a pretty decent show and they post all the citations used in each episode.

        This was referenced: http://www.pbs.org/wgbh/pages/frontline/real-csi/ is a pretty good rundown as well. It includes the case of the guy arrested for the Madrid train bombings based on a fingerprint who had never even been to Spain!

        Also this article was referenced: http://www.psmag.com/politics-and-law/bias-and-the-big-fingerprint-dust-up-3629 dealing with Cognitive unintentional bias in fingerprint matching.

        1. Hognose Post author

          When Andrew drops a hint, he stuffs it in a Mosler safe and drops it on you out of a fifth story window. Miles, time to talk to your local range/gun club…

          I can recommend the seminar without reservation.

          Disclaimer: I was comped the seminar. I should have insisted on paying — it was worth the money — but since I didn’t, the disclaimer must be.

          1. Miles

            Hey, Not knowing how he organized, or scheduled his seminars, I asked.
            Gun Club? What’s that? :) us Hillbillies go out to the back yard, or a neighbor’s field to shoot.

            Andrew, I’ll be working on it. No guarantee of results, or even more interest than me and the old man, but I’ll see who may be interested.

    2. Aaron Spink

      Last I heard, the only forensic method with a strong science backing was DNA. Its also the only forensic tool that started out in general science and was then adopted by forensic science. Pretty much everything else started out as voodoo.

      Oh and everyone’s heard about the issues with the FBI crimelab and hair analysis, right?

  6. Gray

    Andrew and Hognose,

    So given (and I think the same) that science is lacking in the so-called scientific, are defense attorney’s not
    making good Daubert challenges? What allows this junk (apart from the Kultursmog zeitgeist) to not get tossed?

    1. Law of Self Defense

      Look at the first element in Daubert as described above: “(1) whether the evidence can be (and has been) tested” using the scientific method;”

      You’ll look long and hard before you’ll find a criminal trial court judge, or prosecutor, or defense attorney, who if asked would be able to tell you without hesitation what the hell the phrase “scientific method” even means.

      As long as “feels” like “science,” that’s usually good enough.

      It’s pathetic.

      And it leads to circuses like the voice analysis nonsense that went on for weeks prior to the Zimmerman trial. Fortunately, in that case the State’s experts were obviously such loons, and the defense experts so vastly superior, that not even Judge Nelson, despite her tremendous pro-State bias, was able to stomach accepting the State’s experts as “scientific.”

      Of course, at that point, pre-trial, she didn’t yet know how hard the State was going to screw the pooch on their case in chief. HAD she known, I expect she would have allowed that loony “scientific” testimony before the jury.

      –Andrew, @LawSelfDefense

  7. Doug

    Awesomeness!

    Home made 3d Printed Rail Gun:
    http://www.3ders.org/articles/20151018-imgur-user-creates-3d-printed-homemade-railgun.html

    Fires copper plated tungsten, aluminum, carbon and teflon projectiles at speeds of 250m/s.
    Not too shabby. Almost .45acp velocity.
    No mention of projectile weight, but the photos show the slugs. If they are tungsten, they are heavier than 230 grains I’d say.
    Uses six 300J, 350V, 5500uF capacitors with a combined weight of 20lbs, can deliver >1050V and 1.8kJ of energy to a projectile.

    And this is man portable. A bit bulky. But its a first run functioning rifle.
    The sky is the limit on this.
    Since it is uses electromagnetic/plasma propulsion, is it a fire arm in the classic sense?
    Don’t know much about this technology, but it would seem to me it wouldn’t take much to scale the design for more power.

  8. cm smith

    I recently read that new experiments have shown that much that was thought to be known about fire evidence was wrong. “Accelerant burn patterns” were not caused by accelerants, etc.

    1. Hognose Post author

      About 1990, ATF spun up every arson investigator in the country to hunt a super arsonist who was doing arson for hire using solid rocket fuel as his MO. Contains its own oxidant, see.

      I think it was 12 or 15 years later they threw an “oops, our bad” out there without 1% of the fanfare the initial scare got. Nobody ever bagged the rocket fuel arsonist because there wasn’t any, it was all one single analyst’s bad hair day. And for that, every single amateur rocket club and private space startup on the North American continent got raked over the coals.

      Even, given the scientific limitations of the median member of Tribe 1811, investigators working exclusively with liquid fuels. Because who needs a rocket?

  9. archy

    ***Here’s a case in Virginia where the ballistics expert’s testimony amounts to “seeing this ammo used in a murder is rare, rare enough that I’ve only seen it three times-the three murders this trial is about.”***

    He must not have ever heard about the murder of SC Highway Trooper Mark Coates. Probably missed the video, too.

    https://www.youtube.com/watch?v=2FraE77l4fI&safe=active

  10. staghounds

    Almost no criminal cases are identity defences. And among the rare ones that are, there are almost never prints, ballistics, DNA, or the like.

    Full time general jurisdiction prosecutor in a city with 40ish homicides a year here. I’ve handled eight fingerprint cases and two DNA since 1989. There are about 15 of us in the office, so there’s a rough idea of how rare science cases are in state court.

    1. Hognose Post author

      I saw “40 homicides” and I thought, gee, that’s not many (thinking of Chicongo). Then I realized that we average about 20 here in NH. In the whole state. Most of them are in two cities (Manchester and Nashua) and they tend to be impulse control domestics and idjit druggies jacking one another.

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